NEW YORK (Reuters Health) - Women who get some sun during the last trimester of pregnancy may have children with stronger bones, a new study suggests.

UK researchers found that among nearly 7,000 10-year-olds they assessed, those whose mothers were in their last trimester during sunny months tended to have larger bones.

The connection, the researchers say, is presumably explained by vitamin D, which is synthesized in the skin after sun exposure and plays a key role in bone health.

It's possible that mothers' vitamin D levels late in pregnancy have lasting effects on their children's later bone development, the researchers report in the Journal of Clinical Endocrinology and Metabolism.

No one is recommending that pregnant women bask in the sun. Too much UV exposure is a known risk factor for skin cancer.

However, the findings do offer "further justification for strategies intended to improve maternal vitamin D status to optimize skeletal health the child," write researchers Adrian Sayers and Jonathan H. Tobias of the University of Bristol.

Milk and breakfast cereals fortified with vitamin D are among the main food sources of the vitamin. Few foods naturally contain vitamin D, though some fish, like salmon, mackerel and tuna, contain substantial amounts.

Currently, the official recommendation for vitamin D during pregnancy is 200 IU per day, though researchers are still trying to determine what the optimal intake is. A number of studies have suggested that vitamin D deficiency is common in pregnant women.

These latest findings are based on 6,995 British children who underwent bone scans as part of a long-term health study. The researchers used local meteorological data to estimate the mothers' UV exposure during their last trimester.

In general, the study found, children whose mothers had greater sun exposure tended to have larger bones than those whose mothers had less sun exposure.

Bone mass acquired earlier in life is important to fracture risk in later years. If the benefits seen in this study persist into adulthood, Sayers and Tobias note, mothers' vitamin D levels during pregnancy might affect their children's bone health into old age.

SOURCE: Journal of Clinical Endocrinology and Metabolism, March 2009.

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